And God said, Behold, I have given you every herb bearing seed, which is upon the face of all the earth, and every tree, in the which is the fruit of a tree yielding seed; to you it shall be for meat. And to every beast of the earth, and to every fowl of the air, and to every thing that creepeth upon the earth, wherein there is life, I have given every green herb for meat: and it was so.
It is clear from these verses that animals were originally herbivorous and that man was a vegetarian. After the Flood, man was no longer just a vegetarian, as they needed to eat meat while the earth replenished itself. God intended all of mankind to have a balanced diet, as He created all we need, so that we may be sustained on the earth.